Control valve and system

ABSTRACT

A control valve is provided with a pair of modulating valves in parallel flow relation, and each of such modulating valves are generally operable to interrupt the parallel flow relation upon the modulating operation of the other thereof to effect a reduced application through said control valve of fluid pressure supplied thereto.

United States Patent 1 1 Bueler et al.

[ CONTROL VALVE AND SYSTEM [75] Inventors: Richard C. Bueler, Des Peres;

Edward J. Falk, St. Louis, both of [73] Assignee: Wagner ElectricCorporation,

Newark, NJ.

[22] Filed: May 8, 1972 [21] Appl. No.: 250,948

3,659,420 5/1972 Reinecke 303/6 C X Primary Examiner-Richard A. SchacherAttorney-Joseph E. Papin [57] ABSTRACT A control valve is provided witha pair of modulating valves in parallel flow relation, and each of suchmodulating valves are generally operable to interrupt the parallel flowrelation upon the modulating operation of the other thereof to effect areduced application through said control valve of fluid pressuresupplied thereto.

17 Claims, 4 Drawing Figures Patented Oct. 30, 1973 3,768,869

2 Sheets-Sheet 1 CONTROL VALVE AND SYSTEM FIELD OF THE INVENTION Thisinvention pertains generally to brake systems and in particular tocontrol valves for use therein.

BACKGROUND OF THE INVENTION In the past vehicle brake systems, thebraking Capacity between the front and rear axle brakes of a truck ortractor for use with a trailer was usually balanced or divided so thatthe front axle brakes accomplished 25 to 35 percent of the brakingeffort and the rear axle brakes accomplished the other 65 to 75 percentof such braking effort. Due to the Newtonian mechanics of deceleratingor stopping a vehicle which involves the vehicle length of wheel base,static load distribution, and the height of the vehicle center ofgravity from the roadbed, etc., the potential torque increase orincreased braking effort of the front axle brakes due to highdeceleration vehicle stops can be of such magnitude as to result infront to rear axle brake balance, or redistribution of such brakebalance, in the range of 50 percent for the front axle brakes and 50percent for the rear axle brakes or perhaps even greater. In order totake advantage of the front to rear axle brake torque redistribution,front. axle brakes having the capacity to accommodate suchredistribution must be provided on the vehicle, such as front axlebrakes having significantly greater torque or braking effort generatingpotential. When the front axle brakes having the aforementionedsignificantly greater torque or braking effort generating potential wasprovided on the vehicle, the aforementioned redistribution of front torear axle braking efforts effected during rather high vehicledecelerations resulted in the following undesirable or disadvantageousfeatures: (I) an increasing tendency for early front wheel skidding; (2)a deleterious affect on vehicle steerability; (3) a deleteriousimposition of increased loads or forces on the vehicle front suspensioncomponents during braking; and (4) a deleterious imposition ofsignificantly increased loads on the vehicle from tires during brakingwhich results in premature front tire wear. From the foregoing, it isapparent that high levels of front axle brake torque are required toproduce high vehicle deceleration rates, but high levels of front axlebrake torque can only be utilized if high vehicle decelerations wereactually produced; however, this apparent paradox was due to the factthat high vehicle deceleration rates were required to effect sufficientweight transfer to the front axle to effect the utilization of the largemagnitudes of front axle torque.

The principle object of the present invention is to provide a brakesystem and a control valve for use therein which overcomes theaforementioned disadvantageous or undesirable features, and this, aswell as other objects and advantageous features of the presentinvention, will become apparent from the specification which follows.

SUMMARY OF THE INVENTION Briefly, the present invention includes acontrol valve having a pair of modulating means therein in parallel flowrelation, said modulating means each being generally operable tointerrupt said parallel flow relation upon the modulating operation ofthe other thereof to effect a reduced application through said controlvalve of fluid pressure supplied thereto under preselected 2 conditions,respectively. The invention also contemplates a fluid pressure systemhaving the aforementioned control valve interposed therein between afluid pressure supply for said system and a friction device.

RELATED PATENTS This patent application is related to U.S. Pats. Nos.3,278,241 and 3,423,936 issued on Oct. 11, 1966 and Jan. 28, 1969 to W.Stelzer, respectively, but this patent application is a patentablydistinct improvement.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which illustrateembodiments of the present invention and wherein like numerals refer tolike parts wherever they occur:

FIG. 1 is a schematic view of a fluid pressure system embodied in thepresent invention;

FIG. 2 is a sectional view illustrating the control valve of FIG. I alsoembodied in the present invention in cross-section; and

FIG. 3 is a graphical representation illustrating the applied or outputfluid pressure effected by the control valve of FIG. 2 in response tothe supplied or input fluid pressure as compared with a theoretical orideal curve;

FIG. 4 is a partial sectional view illustrating an alternativeconstruction for the metering valve of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings indetail and in particular to FIG. 1, a vehicle fluid pressure or brakesystem 1 is provided with fluid pressure generating means, such as themaster cylinder 2, which is connected by a conduit 3 to a frictiondevice or rear brake 4 of the vehicle rear axle brake set (not shown),and another conduit 5 is connected between the conduit 3 and the inlet 1port of a control valve 6 while the outlet port of said control valve isconnected by a conduit 7 to another friction device or front brake 8 ofthe vehicle front axle brake set (not shown). To complete thedescription of the system 1, it is assumed that the torque or brakingcapabilities of the rear brakes 4' are greater than or at least equal tothat of the front brakes 8.

The control valve 6 is provided with a housing 9 having an upper bore 10axially aligned with stepped counterbores ll, 12, 13, and annularshoulders 14, 15 are provided on said housing between said bore andcounterbore 10, 11 and said counterbores 11, 12, respectively. Inlet andoutlet ports 16, 17 which receive conduits 5, 7 as previously mentioned,are provided in the housing 9 intersecting with the counterbore l2 andthe bore 10, respectively, and a closure member 18 is threadedlyreceived in the leftward or open end of the counterbore 13. The closuremember 18 is provided with a pair of stepped bores 19, 20 having anannular shoulder 21 therebetween, and an annular sealing member or cup22 is seated against said shoulder in sealing engagement with the largerstepped bore 19.

A modulating, metering or proportioning means, such as the piston memberindicated generally at 23 is provided with an annular head or meteringportion 24 having an annular radial flange or retainer portion 25thereon, and peripheral groove means 26 is provided in said head portiondefining an annular metering or proportional shoulder or valve member 27for metering engagement with a cooperating seating member, such as theannular seating or cup member indicated generally at 28 and discussedhereinafter. The proportioning piston 23 is also integrally providedwith opposed reduced portions or extension means 29, 30, and theleftward extension 29 extends coaxially through the closure member cup22 in sealing engagement therewith into sliding and guiding engagementwith the closure member smaller stepped bore 20. The rightward extension30 of the proportioning piston 23 is slidably and guidably received inthe housing bore 10, and an annular shoulder 31 is provided on saidrightward extension for abutting engagement with the housing shoulder 14to define the inoperative, static or at-rest position of saidproportioning piston. A metering or proportioning spring 32 ispre-compressed in abutting engagement between the proportioning pistonretainer 25 and another annular retainer 33 which is press fitted in theinterior end of the closure member larger stepped bore 19, saidproportioning spring normally urging said proportioning piston towardits inoperative position engaging the extension shoulder 31 thereof withthe housing shoulder 14.

The seating member 28 is provided with a centrally located aperture 34extending axially therethrough between opposed side portions 35, 36 ofsaid seating member and radially spaced from the groove 26 of theproportioning piston 23. The seating member side 36 is normally seatedin abutting engagement with the housing shoulder 15 and also defines avalve seat about the seating member aperture 34 for metering engagementwith the metering valve member 27 of the proportioning piston 23. Theseating member 28 is also provided with a peripheral lip 37 in sealingengagement with the housing counterbore 12, and a plurality of axiallyextending return flow passages 38 are provided between the seatingmember side 36 and lip 37, said return flow passages being normallyclosed by the sealing engagement of said lip with said housingcounterbore.

The sealing engagement of the proportioning piston extension 21 with theclosure member seal 22 defines an effective closing area A, on theproportioning piston 23 for subjection to the fluid pressure at theinlet and outlet ports 16, 17, and the sealing engagement of theproportioning piston valve member 27 with the seating member valve seat36 defines an effective area A on said proportioning piston forsubjection to the fluid pressure at said outlet port, as discussedhereinafter.

The housing 9 is also provided with a lower bore 40 which is axiallyaligned with a counterbore 41 having an annular shoulder or valve seat42 therebetween, and connecting passages 43, 44 are interposed betweenthe housing bore 40 and counterbore 12 and the housing bore andcounterbore 41 in parallel flow relation across the proportioning piston23, respectively. A closure member 35 is retained in the rightward endof the housing lower counterbore 41 against displacement by a snap ringand groove assembly 46, and a pair of stepped bores 47, 48 are providedthrough said closure member having an annular shoulder 49 therebetween.

Another modulating, metering or proportioning means, such as the valvedevice indicated generally at 50, is provided with a cup or top-hatshaped element or piston 51 having a radially extending flange or valvemember 52 and a blind bore 53 which is slidably received on the interiorend portion 54 of a stem or rod member 55. The stem 55 is provided withan enlarged or flanged intermediate portion 56 which is slidablyreceived in the closure member larger stepped bore 47, and an annularshoulder 57 is provided on said stem between said intermediate portionand an exterior end portion 58 thereof for abutment with the closuremember shoulder 49, said exterior end portion extending coaxiallythrough the closure member smaller stepped bore 48. A resilient boot 59is provided connecting between the closure member 45, the stem exteriorend portion 58 and the housing counterbore 41 to prevent the entry offoreign particles into the control valve 6. A resilient annular sealingor diaphragm member, indicated generally at 60, is provided withintegral annular inner and outer bead portions 61, 62 interconnected bya flexible diaphragm portion 63, and said inner bead portion is sealablyengaged with the stem intermediate portion 56 being retained thereonagainst displacement by an annular split retainer or compression ring64. The sealing member outer bead 62 is maintained in sealing engagementbetween the interior end of the closure member 45 and the housingcounterbore 41 by a cupshaped retainer member 65 through which the stem55 extends coaxially, and said retainer member is biased into engagementwith the outer bead 62 by the compressive force of a metering orproportioning spring 66 engaged therewith.

A valve plate or metering piston member 67 is slidably received in thehousing counterbore 41 being urged toward engagement with the housingshoulder 42 by the metering spring 66, and a centrally located bore 68is provided in said piston member being slidably received on the stem55, said stem having a snap ring and groove assembly 69 thereon definingan abutment predeterminately spaced from said valve plate forvdriving orabutting engagement therewith about said bore. A recess 70 is providedin the piston member 67, and an annular seal or metering valve member 71having a central aperture or passage means 72 therethrough is providedin said recess being normally urged into sealing engagement with itscooperative housing shoulder or valve seat 42. A plurality of otheraperture or passage means 73 are axially provided through the pistonmember 67 normally in open pressure fluid communication with the valveaperture 70 and the inlet and outlet ports 16, 17 when the valve member52 of the tophat element 51 is displaced from sealing engagement withthe valve member 71 which defines a cooperating seat about its passage72 for said valve member 52.

The diaphragm member 60 is provided with an annular effective area Adefined between the bending or flexing radius thereof and the sealingengagement of its inner bead 67 with the stem 55, and said stem is alsoprovided with an effective area A defined by the sealing engagementthereof with said diaphragm member inner head, said areas A A, beingsubjected to the fluid pressure at the outlet port 17. Another annulareffective area A is defined on the piston member 67 by the sealingengagement of the metering valve member 71 with the housing valve seat42, and said area A is subjected to the fluid pressure at the inlet andoutlet ports 16, 17, respectively, as discussed hereinafter.

To complete the description of the control valve 6, it should be notedthat the housing upper bore 10 and counterbores 11, 12 define a flowpassage, indicated generally at B, between the inlet and outlet ports16, 17 which is controlled by the proportioning valve 23, and thehousing lower bore and counterbore 40, 41 and connecting passages 43, 44define another flow passage, indicated generally at C, which isconnected in parallel or shunt flow relation with the flow passage Bbetween said inlet and outlet ports, said flow passage C beingcontrolled by the metering device 50.

OPERATION in the operation with the component parts of the system 1 andcontrol valve 6 positioned as shown in the drawings and as describedhereinbefore, a supplied or input fluid pressure P is transmitted uponoperator acmatron of the master cylinder 2 through the conduit 3 toeffect energization of the vehicle rear brake 4 and also through theconduit 5 to the inlet port 16 of said control valve. The supplied fluidpressure P flows from the inlet port 16 through the housing uppercounterbore 12, the seating member aperture 34, the counterbore 11 andthe bore to establish an output or applied fluid pressure P'o at theoutlet port 17, and the applied fluid pressure Po thereafter flowsthrough the conduit 7 to effect energization of the vehicle front brake8 substantially simultaneously with the aforementioned energization ofthe vehicle rear brake 4. It should be noted that the parallel flowpassage C also may provide for the flow of the supplied fluid pressure Pfrom the housing upper counterbore 12 through the connecting passage 43,the housing lower bore 40, the metering piston apertures 72, 73, thecounterbore 41 and the connecting passage 44 to the upper bore 10 andoutlet port 17, and, of course, the supplied fluid pressure P willchoose the one of the parallel flow paths B, C which offers the leastresistance to its flow through the control valve 6.

The supplied fluid pressure P acts on the effective closing area A, ofthe proportioning piston 23 to establish a closing force P A, tending tourge said proportioning piston against the compressive force Fc of theproportioning spring 32, and the supplied fluid pressure P also acts onthe effective closing area A A, of the metering device 50 to establishanother closing force P (A, A however, the proportioning spring force Feand the inherent resiliency of the diaphragm member 60 oppose movementof said .proportioning piston and the stem 55 of said metering deviceuntil the applied fluid pressure P attains a predetermined value M asshown on the line OS in the graph of FIG. 3.

When the predetermined value M of the supplied fluid pressure P isattained, the closing forces P A,, P (A, A,,) overcomes theproportioning spring force Fe and the inherent resiliency of thediaphragm member 60, and in this manner, the proportioning piston 23 ismoved leftwardly toward an isolating position engaging the valve member27 with the seating member valve seat 36 and the stem 55 is movedrightwardly to drivingly engage the abutment 69 thereof with themetering piston 67 and move the valve member 51 into sealing engagementwith the metering piston valve seat 71; therefor, the engagement-of theproportioning piston valve member 27 with the seating member valve seat36 and the sealing engagement of the valve member 51 with the meteringpiston valve seat 71 interrupts pressure fluid communication through theparallel flow paths B and C between the inlet and outlet ports 16, 17,respectively. Upon the engagement of the proportioning piston valvemember 27 with the seating member valve seat 36, the supplied fluidpressure P acts on the effective input area A, A, of the proportioningpiston 23 to establish an input force P (A, A,) which is additive to theproportioning spring force F0 to substantially balance the opposedoutput force Po A established by the applied fluid pressure P0 at theoutlet port 17 acting on the effective output area A, of saidproportioning piston.

From the graphical representation in FIG. 3, it is obvious that anincrease in the magnitude of the supplied fluid pressure P in excess ofthe predetermined value M, as shown by the line OS, will result inproportionally reduced increases in the applied fluid pressure P0, asshown by the line MN. For instance, when the supplied fluid pressure Pis increased to a value in excess of the predetermined value M but lessthan the predetermined value T, the input force P (A -A,) iscorrespondingly increased and additive to the proportioning spring forceF0 to overcome the output force P0 A therefor, the proportioning piston23 is moved in a rightwardly direction toward a metering positiondisengaging the valve member 27 thereof from the seating member valveseat. 36 to effect a metered application of the supplied fluid pressureP from the counterbore 12 through the seating member aperture 34, thecounterbore 11 and the bore 10 to the outlet port 17 to effect aproportional increase of the applied fluid pressure P0 at the outletport 17 in a predetermined ratio with the supplied fluid pressure P atthe inlet port 16, as shown by, the line MN in the graph of FIG. 3wherein: P0 [P (A A Fc]/A Of course,'the increased applied fluidpressure P0 effects a corresponding increase in the output force P0 Aand when the increased output force P0 A attains an increased valuesubstantially equal to that of the increased input force P (A A and theadditive proportioning spring force Fc, the proportioning piston 23 isagain moved toward its isolating position to re-engage the valve member27 with the seating member valve seat 36 to again isolate the increasedsupplied and applied fluid pressures P, Po. It is, of course, obviousthat the proportioning piston 23 will be responsive to further increasesin the supplied fluid pressure P to effect further correspondingproportional increases in the applied fluid pressure P0 in the samemanner as previously described above, until the supplied and appliedfluid pressures P, Po respectively attain the predetermined val- Y ues Tand N.

. With the metering device in its isolating position having the valvemember 51 engaged with the metering piston seal 71, as previouslymentioned, the increased supplied and applied fluid pressures P, Po atthe inlet and outlet ports 16, 17 act on the effective additive area A,A, and A A of the metering device 50 to establish an input force P (A +AP0 (A A and.

an opposing output force P0 A respectively. From the graphicalrepresentation in FIG. 3, it is obvious that further increases in themagnitude of the supplied fluid pressure in excess of the predeterminedvalue T, as shown on the line 05, will result in a proportionallyincreasing increase in the output fluid pressure Po, as shown by theline NR. For instance, when the supplied fluid pressure P is increasedto a value in excess of the predetermined value T but less than thepredetermined value R, the input force P (A, A P0 (A A iscorrespondingly increased to overcome the output force Po A and theadditive compressive force Fs of the metering spring 66; therefore, thevalve member 51, metering piston 67 and stem are concertedly movable ina rightward direction toward a metering position disengaging themetering piston valve member 71 from its cooperating housing valve seat42 to effect a further metered application of the supplied fluidpressure P from the housing lower bore 40 through the lower counterbore41 and connecting passage 44 to the outlet port 17 to effect a furtherproportional increase of the applied fluid pressure P in a predeterminedratio with the supplied fluid pressure P at the inlet port 16, as shownby the line NR in the graph of FIG. 3 wherein: P0 [P (A A Fs]/2A A Ofcourse, the increased applied fluid pressure Po effects a correspondingincrease in the output force P0 A and when the increased output force P0A and the additive metering spring force Fs attains an increased valuesubstantially equal to that of the increased input force P 4 P0 (A A themetering device 50 is again moved leftwardly toward its isolatingposition to re-engage the metering piston valve member 71 with thehousing valve seat 42 to again isolate the increased supplied andapplied fluid pressures P, Po. It is, of

course, obvious that the metering device 50 will be responsive tofurther increases in the supplied fluid pressure P to effect furthercorresponding proportional increases in the applied fluid pressure P0,in the same manner as previously described, until the supplied andapplied fluid pressures P, P0 respectively attain magnitudes of thepredetermined value R, as shown on the line OS. When the supplied andapplied fluid pressures P, P0 attain the predetermined value R, theinput force P (A A P0 (A A attains a magnitude which overcomes theadditive metering spring and output forces Fs and P0 A wherein the valvemember 51, the stem 55 and the metering piston 67 are concertedlymovable in a rightward direction toward an open position effecting anequalizing or open pressure fluid communication between the inlet andoutlet ports 16, 17 through the upper housing counterbore 12, theconnecting passage 43, the housing lower bore and counterbore 41 and theconnecting passage 44. In this manner, when the metering device 50 is inits open position, the supplied and applied fluid pressures P, P0 areagain blended at magnitudes thereof in excess of the predetermined valueR, as shown by the line RS in the graph of FIG. 3.

When the master cylinder 2 is deactuated, the supplied fluid pressure Pis vented to the atmosphere which effects de-energization of the rearbrake 4 and eliminates the input force P (A A acting on theproportioning piston 23 as well as eliminating the force P (A A actingon the metering device 55. Upon the reduction of the supplied fluidpressure P to a value less than the predetermined value R on the line OSin the graph of FIG. 3 in response to the deactuation of the mastercylinder 2, the force Fs of the metering spring 66 concertedly urges thevalve member 51, the step 55 and metering piston 67 leftwardly tore-engage the metering valve member 71 with the housing valve seat 42which momentarily interrupts pressure fluid communication through theflow passage C again isolating the.

supplied and applied fluid pressures P, Po since the proportioning valve23 is also in its isolating position. When the supplied fluid pressure Pis further reduced to a value less than that of the isolated appliedfluid pressure Po, a pressure differential is established across thevalve member 51 of the metering device 50 which is effective to movesaid valve member leftwardly toward a position disengaged from themetering valve member 71 to open the metering piston apertures 72, 73and effect the return flow therethrough of the isolated fluid pressureP0 from the outlet port 17 to the inlet port 16. In this manner, theopen pressure fluid communication through the flow passage C for thereturn flow of the applied fluid pressure P0 eliminates the appliedfluid pressure and also the force P0 (A A acting on the metering device50 which permits the diaphragm member 60 and stem 55 to also return totheir original positions as shown in the drawings.

It should be noted that the return flow of the applied fluid pressure P0from the outlet port 17 to the inlet port 16 may be effected througheither of the parallel flow passages B, C, depending, of course, uponwhich of the proportioning valve or metering device 23, 50 offers theleast resistance in said flow passages to said return flow. Forinstance, if the proportioning valve 23 offered less resistance to thereturn flow of the applied fluid pressure P0, it may alternativelyreturn through the flow passage B instead of the flow passage C, aspreviously described. In this event, when the supplied fluid pressure Pis eliminated upon the deactuation of the master cylinder 2, aspreviously discussed, the applied fluid pressure P0 acting on theseating member 28 displaces the sealing lip 37 thereof from sealingengagement with the housing counterbore 12 to open the return flowpassages 38 across said seating member, and in this manner, the appliedfluid pressure P0 returns from the outlet port 17 through the housingupper bore 10, the counterbore 11, the open return flow passages 38, andthe counterbore 12 to the inlet port 16 and therefrom through theconduits 5, 3, to the master cylinder 2. When the applied fluid pressureP0 is so reduced to correspondingly reduce the output force P0 A to avalue less than the proportioning spring force Po, the proportioningspring 32 moves the proportioning piston 23 rightwardly to its originalor inoperative position re-engaging the abutment 31 thereof with thehousing shoulder 14 and disengaging the valve member 27 from the seatingmember valve seat 36 to again open the seating member aperture 34re-establishing open pressure fluid communication therethrough betweenthe inlet and outlet ports 16, 17 to effect complete elimination of theapplied fluid pressure Po.

It is apparent that the shape, i.e. the bellying", of the ideal curve 0Gin the graph of FIG. 3 for the front brake 8 will depend upon theNewtonian mechanics of the vehicle, such as the length of the vehiclewheel base, static load distribution between the vehicle front and rearaxles, and the height of the vehicle center of gravity for instance, andas the vehicle deceleration approaches its maximum rate (which isassumed for our purposes to be in the range of a one G deceleration),the front brake torque requirement increases appreciably. Of course, thegreat majority of vehicle decelerations or stops are not of the one Gvariety but instead are in the deceleration range indicated generally'bythe line OMN in the graph of FIG. 3; therefore, it'is apparent that thecontrol valve 6 functions in the system 1, as previously described, notonly to effect an actual curve OMNRS closely approximating the idealcurve but also functions to proportion the applied or output fluidpressure Po delivered to the front brakes 8 and limit the amount oftorque developed thereby in the rather low vehicle deceleration rangeindicated generally by the line OMN. In the higher or more intensevehicle deceleration range indicated by the line NRS in the graph ofFIG. 3 when the Newtonian mechanics of vehicle braking come into play tosuch an extend effecting an appreciable vehicle weight shift wherein thefront brakes 8 must necessarily assume more of the vehicle brakingeffort, Le. a redistribution of the front to rear axle brake balance, itis apparent that the control valve 6 then functions in the systems 1, aspreviously described, not only to increase the applied fluid pressure Pdelivered to the front brakes 8 which eventually blends with thesupplied fluid pressure P but also to increase the torque effected bysuch front brakes to accommodate the inertia weight shift and front torear axle brake balance redistribution when vehicle decelerationsapproaching the one G range are effected.

Referring now to FIG. 4, an alternative construction of the meteringdevice 50a is shown having substantially the same component parts andfunctioning in the system 1 in substantially the same manner as themetering device 50 of the control valve 6 with the following exceptions.

The metering piston 67a of the metering device 50a is slidably receivedin the housing lower counterbore 41 having a recess 70a in which isreceivedan annular seal or valve member 71a, and the force Fs of themetering spring 66 acting on the proportioning piston 67a normally urgesthe valve member 71a into sealing engagement with the housing valve seat42 interrupting pressure fluid communication through the flow passage Cbetween the inlet and outlet ports l6, 17. Another sealing member orO-ring 80 is carried in the bore 68a of the metering piston 67a insealing engagement with the periphery of the stem 55a which extendscoaxially therethrough, and a snap ring and groove assembly 69a isprovided in said stern adjacent to the free end 54a thereof in drivingor abutting engagement with said metering piston.

In the operation of thecontrol valve 6 utilizing the I metering device50a, said metering device is responsive to supplied and applied fluidpressures in excess of the predetermined values T and N, respectively,as shown in the graph of FIG. 3. When the applied fluid pressure P isincreased to a value in excess of the predetermined value T but lessthan the predetermined value R, the input force F (A, A) P0 (A A iscorrespondingly increased to overcome the opposing output force P0 A towhich the force Fs of the metering spring 66 is additive; therefore, themetering piston 67a and stem 55a are concertedly movable in therightward direction toward a metering position disengaging the meteringpiston valve member 71a from the housing valve seat 42 to effect furthermetered application of the supplied fluid pressure P from the housinglower bore 40 through the lower counterbore 41 and connecting passage tothe outlet port 17 to effect a further proportionally metered increasein the applied fluid pressure P0 in the same predetermined ratio as setforth hereinbefore with respect to the metering device 50. When thesupplied and applied fluid pressures P, Po attain the predetermined R,as shown on the line OS in the graph of H6. 3, the input force P (A, APo (A A attains a magnitude which overcomes the additive metering springand output forces Fs, P0 A wherein the metering piston 67a and stem 55aare concertedly movable in a right-ward direction toward an openposition effecting equalizing or open pressure fluid communicationbetween the inlet and outlet ports 16, 17 through the flow passage Cwherein the supplied and applied fluid pressures P, P0 are once againblended, as shown by the line RS in the graph of FIG. 3.

When the supplied and applied fluid pressures P, P0 are reduced tovalues less than the predetermined value R upon the deactuation of themaster cylinder 2, as previously discussed, the force Fs of the meteringspring 66'overcomes the corresponding reduced input force P (A, A P0 (AA to return the metering piston valve 71a toward its isolating positionengaged with the housing valve seat 42 closing the flow passage C. Uponfurther reduction of the supplied fluid pressure, the return flow of theapplied fluid pressure from the outlet port 17 to the inlet port 16 iseffected by the proportioning piston 23 only through the flow passage Bin the same manner as previously described hereinbefore.

From the foregoing, it is now apparent that a novel system 1 and controlvalve 6 are disclosed and that changes or modifications so as to theprecise connections, configurations, shapes or details ofthe'constructions set forth herein by way of illustration may be made bythose skilled in the art without departing from the spirit of theinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A control valve comprising a housing, a pair of modulating meansmovable in said housing in parallel flow relation for performingmodulating operations on fluid pressure supplied thereto andinterrupting said parallel flow relation under preselected conditions,respectively,each of said modulating means being generally operable tointerrupt said parallel flow relation upon the modulating operation ofthe other thereof to effect applications through said housing of reducedfluid pressures in different predetermined ratios with the suppliedfluid pressure, respectively, and one of said modulating means includingmeans responsive to the supplied and applied fluid pressure of a commonpredetermined value to thereafter effect the blending of the suppliedand applied fluid pressures.

2. A control valve comprising a housing, a pair of flow passages in saidhousing and connected in parallel flow relation, a pair of modulatingmeans movable in said flow passages for performing modulating operationson fluid pressure supplied thereto and interrupting flow thereof throughsaid flow passages upon preselected conditions, respectively, each ofsaid modulating means being generally operable to interrupt flow of thesupplied fluid pressure through said flow passages upon the modulatingoperation of the other of said modulating means to effect applicationsthrough said flow passages of reduced fluid pressures in differentpredetermined ratios with the supplied fluid pressure, respectively, andone of said modulating means including means responsive to the suppliedand applied fluid pressures of a predetermined value to open one of saidflow passages and effect an unmodulated flow therethrough of thesupplied fluid pressure.

3. A control valve comprising a housing, proportioning means andmetering means movable in said housing in parallel flow relation forperforming proportioning and metering operations on fluid pressuresupplied thereto and for interrupting said parallel flow relation underpreselected conditions, respectively, said proportioning means beingoperable generally in response to the supplied fluid pressure betweenfirst and second predetermined values to effect the application throughsaid housing of a reduced fluid pressure in a predetermined ratio withthe supplied fluid pressure when said metering means is interruptingsaid parallel flow relation, and said metering means being thereaftergenerally operable in response to the supplied fluid pressure in excessof the second predetermined value and the applied fluid pressure actingthereon to effect a metering application through said housing of thesupplied fluid pressure to increase the applied fluid pressure inanother predetermined ratio with the supplied fluid pressurepredeterminately greater than the first named predetermined ratio whensaid proportioning means is interrupting said parallel flow relation,and said metering means including means responsive to the supplied andapplied fluid pressures of a third predetermined value predeterminatelygreater than the second predetermined value to thereafter effect anunmetered flow through said housing of the supplied fluid pressure.

4. A control valve according to claim 3, comprising a pair of flowpassages in said housing and connected in parallel flow relation, saidproportioning and metering means being movable in said flow passages andcontrolling the applications therethrough of the supplied fluidpressure, respectively.

5. A control valve according to claim 4, wherein said included meansopens one of said flow passages to effect the unmetered flowtherethrough of the supplied fluid pressure when the supplied andapplied fluid pressures attain the third predetermined value.

6. A control valve according to claim 4, wherein said proportioningmeans includes resiliently urged means movable in one of said flowpassages, said resiliently urged means being movable against its ownforce in response to the supplied fluid pressure of the firstpredetermined value acting thereon toward a flow interrupting positionin said one passage means and being further movable assisted by its ownforce in response to increases in the supplied fluid pressure in excessof the first predetermined value toward another position effecting theincrease in the applied fluid pressure in the first named predeterminedratio, and said resiliently urged means retaining its flow interruptingposition in said one flow passage when the supplied fluid pressureexceeds the second predetermined value to effect the metering operationof said metering means in the other of said flow passages.

7. A control valve according to claim 6, wherein said resiliently urgedmeans includes piston means movable in said one passage means, andresilient means engaged with saidpiston means, said piston means beingmovable against said resilient means in response to the supplied fluidpressure of the first predetermined value acting on said piston meanstoward its flow interrupting position closing said one passage means andbeing thereafter further movable assisted by said resilient means inresponse to the increased supplied fluid pressure in excess of saidfirst predetermined value and less than said second predetermined valuetoward its other position effecting the increase in the applied fluidpressure in the first named ratio, and said piston means maintaining itsflow interrupting position in said one flow passage when the suppliedfluid pressure exceeds the second predetermined value effecting themetering operation of said metering means in said other flow passage.

8. A control valve according to claim 4, comprising seating means insaid housing about said one flow passage, and valve means on said pistonmeans for engagement with said seating means, said valve means beingengaged with said seating means to close said one passage means whensaid piston means is in its flow interrupting position and said valvemeans being disengaged from said seating meansupon the movement of saidpiston means toward its to applied position.

9. A control valve according to claim 4, wherein said metering meansalso includes resiliently urged means movable on one of said flowpassages, and said included means defines a pair of additive effectiveareas on said resiliently urged means for respective subjection to thesupplied and applied fluid pressures in said flow passages, saidresiliently urged means being movable against its own force from itsflow interrupting position in said one flow passage in response to thesupplied fluid pressure in excess of the second predetermined value andthe applied fluid pressure respectively acting on said areas toward ametering position effecting the metered increase in the applied fluidpressure in the other predetermined ratio with the supplied fluidpressure, and said resiliently urged means also being movable againstits own force toward an open position in said one flow passage effectingthe unmetered flow therethrough of the supplied fluid pressure when thesupplied and applied fluid pressures respectively acting on said areasattain the third predetermined value.

10. A control valve according to claim 9, wherein said resiliently urgedmeans include piston means movable in said one flow passage, resilientmeans engaged with said piston means, one of said areas being on saidpiston means and subjected to the supplied fluid pressure, diaphragmmeans in said housing subjected to the applied fluid pressure forconnection with said piston means and defining the other of said areas,said piston means being movable from its flow interrupting positionagainst said resilient means in response to the supplied fluid pressurein excess of the second predetermined value acting on said one area andthe applied fluid pressure acting on said other area toward its meteringposition, and said piston means also being movable toward its openposition against said resilient means when the supplied and appliedfluid pressures respectively acting on said one and other areas attainsthe third predetermined value.

11. A control'valve according to claim 10, comprising a valve seat insaid housing about said one flow passage, and valve means on said pistonmeans for engagement with said valve seat, said valve means beingengaged with said valve seat to close said one flow passage when saidpiston means is in its flow interrupting position and said valve meansbeing disengaged from said valve seat upon the movement of said pistonmeans toward its metering and openpositions.

12. A control valve according to claim 3, comprising passage means insaid metering means for the passage therethrough of the supplied fluidpressure less than the first predetermined value, a valve seat on saidmetering value to move said valve means toward engagement with saidvalve seat and close said passage means when said metering means is inits flow interrupting position.

13. A control valve comprising a housing having inlet and outlet portstherein, a pair of passage means in said housing connected in parallelflow relation between said inlet and outlet ports, a proportioning valveand a metering valve respectively movable in said passage means forcontrolling pressure fluid communication between said inlet and outletports, said proportioning valve being movable in response to fluidpressure at said inlet port in excess of a first predetermined value andless than a second predetermined value from a position interruptingpressure fluid communication through one of said passage means toward aposition effecting metered pressure fluid communication therethrough toestablish a reduced fluid pressure at said outlet port in apredetermined ratio with that at said inlet portion when said meteringvalve is in a position interrupting pressure fluid communication throughthe other of said passage means, said metering valve being thereaftermovable from its pressure fluid communication interrupting position insaid other passage means in response to fluid pressure at said inletport in excess of the second predetermined value and reduced fluidpressure at said outlet port acting thereon toward a position effectingmetered pressure fluid communication through said other flow passage toincrease the reduced fluid pressure at said outlet portion in anotherpredetermined ratio with that at said inlet port predeterminatelygreater than said first named predetermined ratio when saidproportioning valve is in its pressure fluid communication interruptingposition, and said metering valve including means responsive to thefluid pressures at said inlet and outlet portions of a thirdpredetermined value to move said metering means toward an open positionin said other passage means effecting unmetered pressure fluidcommunication therethrough between said inlet and outlet ports.

14. A control valve comprising a housing having inlet and outlet portstherein, first and second passage means in said housing and respectivelyconnected in parallel flow relation between said inlet and outlet ports,first and second valve seats in said housing about said first and secondpassage means, first and second piston means movable in said first andsecond passage means for controlling pressure fluid communicationtherethrough between said inlet and outlet ports, re-

' spectively, first and second valve means on said first and secondpiston means for engagement with said first and second valve seats,first and second spring means engaged with said first and second pistonmeans, said second spring means urging said second piston means toward aposition engaging said second valve means with said second valve seatfor interrupting pressure fluid communication through said secondpassage means between said inlet and outlet ports, said first pistonmeans being initially movable against said first spring means inresponse to fluid pressure at said inlet and outlet ports of a firstpredetermined value to engage said first valve means with said firstvalve seat interrupting pressure fluid communication between said inletand outlet ports through said first passage means and said first pistonmeans also being thereafter further movable assisted by said firstspring means in response to fluid pressure at said inlet port in excessof the first predetermined value and less than a second predeterminedvalue to disengage said first valve means from said first valve seateffecting metered pressure fluid communication through said firstpassage means between said inlet and outlet ports and establishing ametered fluid pressure at said outlet port in a first predeterminedratio with that at said inlet port when said second piston means is inits pressure fluid communication interrupting position, a pair ofeffecting areas-on said second piston means respectively subjected tothe fluid pressures at said inlet and outlet ports, said second pistonmeans being movable from its pressure fluid communication interruptingposition against said second spring means in response to the fluidpressure at said inlet port in excess of the second predetermined valueacting on one of said areas and the reduced metered fluid pressure atsaid outlet port acting on the other of said areas to disengage saidsecond valve means from said second valve seat effecting meteredpressure fluid communication between said inlet and outlet ports throughsaid second passage means and establishing an increased metered fluidpressure at said outlet port in y a second predetermined ratio with thatat said inlet .port

wherein said second predetermined ratio is'predeterminately greater thansaid first predetermined ratio when said first piston means is in itspressure fluid communication interrupting position, and said secondpiston means also being further movable against said second spring meansto disengage said second valve means from said second valve seat andestablish open pressure fluid communication through said second passagemeans between said inlet and outlet ports when the fluid pressure atsaid inlet port and the metered fluid pressure at said outlet portacting on said one and other areas attain a third predetermined valuepredeterminately greater than said second predetermined value,respectively.

15. A fluid pressure system comprising a friction device, a fluidpressure source for energizing said friction device, a pair ofmodulating means in parallel flow relation in said system for performingmodulating operation on fluid pressure supplied from said source to saidfriction device under preselected conditions, each of said modulatingmeans being generally operable to interrupt the parallel flow relationwhen the other thereof is performing its modulating operation,respectively.

16. A fluid pressure system comprising at least one friction device, afluid pressure source for supplying fluid pressure to said frictiondevice to effect energization thereof, a pair of modulating meansconnected between said source and friction device in parallel flowrelation for performing modulating operations on fluid pressure suppliedfrom said source to said friction device under preselected conditions,each of said modulating means being generally operable to interrupt theparallel flow relation upon the modulating operation of r the otherthereof to effect the application to said friction device of thesupplied fluid pressure in different predetermined ratios, respectively,and one of said modulating means including means responsive to thesupplied fluid pressure in excess of a predetermined value to obviatethe modulating operation of said one modulating means.

- 17. A fluid pressure system comprising at least one fluid pressureresponsive brake device, means including a fluid pressure source forsupplying fluid pressure to said brake device to effect energizationthereof, proportioning means and metering means connected in parallelflow relation with each other between said source and brake device forperforming proportioning and metering operations on the supplied fluidpressure and for interrupting said parallel flow relation underpreselected conditions, respectively, said proportioning mined ratiowith the supplied fluid pressure predeterminately greater than the firstnamed predetermined ratio when said proportioning means is interruptingsaid parallel flow relation, and said metering means including meansresponsive to the supplied and applied fluid pressures of a thirdpredetermined value predeterminately greater than the secondpredetermined value for obviating the metering operation of saidmetering means and effecting an unmetered flow of the supplied fluidpressure to said brake device.

, UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.768, 869 Dated October 30, 1973 Inventofls) Richard C. Bueler andEdward J. Falk It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 6, line 31, "P (A A1)" should read P (A2 A1) Column 7, line 53,"step" should read stem Column 9, line 58, P (Ar Ag) Po (A3 A5)" shouldread P (A4 A5) Po 3 A5) Column ll, line 6, "ing" should read ed Column12, line 5, delete "to applied" and insert other line 62, "toapplied"should read to applied Column 13, line l4, "portion" should read portline 24, 'portion" should read port line 30, "portions" should readports Column 14, line 36, "tion" should read tions Signed- 'and sealedthis 16th day of July l9'7lp. p

(SEAL) Attest:

MCCOY GIBSON, JR. c. MARSHALL DANN Attesting Officer a Commissioner ofPatents i, FORM PC4050 0459) 1 uscoMM-oc 60376-P69 I fi U.5. GOVERNMENTPRINTING OFFICE 1' "I, 0-36-J3l,

1. A control valve comprising a housing, a pair of modulating meansmovable in said housing in parallel flow relation for performingmodulating operations on fluid pressure supplied thereto andinterrupting said parallel flow relation under preselected conditions,respectively, each of said modulating means being generally operable tointerrupt said parallel flow relation upon the modulating operation ofthe other thereof to effect applications through said housing of reducedfluid pressures in different predetermined ratios with the suppliedfluid pressure, respectively, and one of said modulating means includingmeans responsive to the supplied and applied fluid pressure of a commonpredetermined value to thereafter effect the blending of the suppliedand applied fluid pressures.
 2. A control valve comprising a housing, apair oF flow passages in said housing and connected in parallel flowrelation, a pair of modulating means movable in said flow passages forperforming modulating operations on fluid pressure supplied thereto andinterrupting flow thereof through said flow passages upon preselectedconditions, respectively, each of said modulating means being generallyoperable to interrupt flow of the supplied fluid pressure through saidflow passages upon the modulating operation of the other of saidmodulating means to effect applications through said flow passages ofreduced fluid pressures in different predetermined ratios with thesupplied fluid pressure, respectively, and one of said modulating meansincluding means responsive to the supplied and applied fluid pressuresof a predetermined value to open one of said flow passages and effect anunmodulated flow therethrough of the supplied fluid pressure.
 3. Acontrol valve comprising a housing, proportioning means and meteringmeans movable in said housing in parallel flow relation for performingproportioning and metering operations on fluid pressure supplied theretoand for interrupting said parallel flow relation under preselectedconditions, respectively, said proportioning means being operablegenerally in response to the supplied fluid pressure between first andsecond predetermined values to effect the application through saidhousing of a reduced fluid pressure in a predetermined ratio with thesupplied fluid pressure when said metering means is interrupting saidparallel flow relation, and said metering means being thereaftergenerally operable in response to the supplied fluid pressure in excessof the second predetermined value and the applied fluid pressure actingthereon to effect a metering application through said housing of thesupplied fluid pressure to increase the applied fluid pressure inanother predetermined ratio with the supplied fluid pressurepredeterminately greater than the first named predetermined ratio whensaid proportioning means is interrupting said parallel flow relation,and said metering means including means responsive to the supplied andapplied fluid pressures of a third predetermined value predeterminatelygreater than the second predetermined value to thereafter effect anunmetered flow through said housing of the supplied fluid pressure.
 4. Acontrol valve according to claim 3, comprising a pair of flow passagesin said housing and connected in parallel flow relation, saidproportioning and metering means being movable in said flow passages andcontrolling the applications therethrough of the supplied fluidpressure, respectively.
 5. A control valve according to claim 4, whereinsaid included means opens one of said flow passages to effect theunmetered flow therethrough of the supplied fluid pressure when thesupplied and applied fluid pressures attain the third predeterminedvalue.
 6. A control valve according to claim 4, wherein saidproportioning means includes resiliently urged means movable in one ofsaid flow passages, said resiliently urged means being movable againstits own force in response to the supplied fluid pressure of the firstpredetermined value acting thereon toward a flow interrupting positionin said one passage means and being further movable assisted by its ownforce in response to increases in the supplied fluid pressure in excessof the first predetermined value toward another position effecting theincrease in the applied fluid pressure in the first named predeterminedratio, and said resiliently urged means retaining its flow interruptingposition in said one flow passage when the supplied fluid pressureexceeds the second predetermined value to effect the metering operationof said metering means in the other of said flow passages.
 7. A controlvalve according to claim 6, wherein said resiliently urged meansincludes piston means movable in said one passage means, and resilientmeans engaged with said piston means, said piston means being movableagainst saiD resilient means in response to the supplied fluid pressureof the first predetermined value acting on said piston means toward itsflow interrupting position closing said one passage means and beingthereafter further movable assisted by said resilient means in responseto the increased supplied fluid pressure in excess of said firstpredetermined value and less than said second predetermined value towardits other position effecting the increase in the applied fluid pressurein the first named ratio, and said piston means maintaining its flowinterrupting position in said one flow passage when the supplied fluidpressure exceeds the second predetermined value effecting the meteringoperation of said metering means in said other flow passage.
 8. Acontrol valve according to claim 4, comprising seating means in saidhousing about said one flow passage, and valve means on said pistonmeans for engagement with said seating means, said valve means beingengaged with said seating means to close said one passage means whensaid piston means is in its flow interrupting position and said valvemeans being disengaged from said seating means upon the movement of saidpiston means toward its other position.
 9. A control valve according toclaim 4, wherein said metering means also includes resiliently urgedmeans movable on one of said flow passages, and said included meansdefines a pair of additive effective areas on said resiliently urgedmeans for respective subjection to the supplied and applied fluidpressures in said flow passages, said resiliently urged means beingmovable against its own force from its flow interrupting position insaid one flow passage in response to the supplied fluid pressure inexcess of the second predetermined value and the applied fluid pressurerespectively acting on said areas toward a metering position effectingthe metered increase in the applied fluid pressure in the otherpredetermined ratio with the supplied fluid pressure, and saidresiliently urged means also being movable against its own force towardan open position in said one flow passage effecting the unmetered flowtherethrough of the supplied fluid pressure when the supplied andapplied fluid pressures respectively acting on said areas attain thethird predetermined value.
 10. A control valve according to claim 9,wherein said resiliently urged means include piston means movable insaid one flow passage, resilient means engaged with said piston means,one of said areas being on said piston means and subjected to thesupplied fluid pressure, diaphragm means in said housing subjected tothe applied fluid pressure for connection with said piston means anddefining the other of said areas, said piston means being movable fromits flow interrupting position against said resilient means in responseto the supplied fluid pressure in excess of the second predeterminedvalue acting on said one area and the applied fluid pressure acting onsaid other area toward its metering position, and said piston means alsobeing movable toward its open position against said resilient means whenthe supplied and applied fluid pressures respectively acting on said oneand other areas attains the third predetermined value.
 11. A controlvalve according to claim 10, comprising a valve seat in said housingabout said one flow passage, and valve means on said piston means forengagement with said valve seat, said valve means being engaged withsaid valve seat to close said one flow passage when said piston means isin its flow interrupting position and said valve means being disengagedfrom said valve seat upon the movement of said piston means toward itsmetering and open positions.
 12. A control valve according to claim 3,comprising passage means in said metering means for the passagetherethrough of the supplied fluid pressure less than the firstpredetermined value, a valve seat on said metering means about saidpassage means, valve means on said metering means for engagement withsaid valve seat, saiD included means including diaphragm means subjectedto the applied fluid pressure and connected with said valve means, saiddiaphragm means being responsive to applied fluid pressure of the firstpredetermined value to move said valve means toward engagement with saidvalve seat and close said passage means when said metering means is inits flow interrupting position.
 13. A control valve comprising a housinghaving inlet and outlet ports therein, a pair of passage means in saidhousing connected in parallel flow relation between said inlet andoutlet ports, a proportioning valve and a metering valve respectivelymovable in said passage means for controlling pressure fluidcommunication between said inlet and outlet ports, said proportioningvalve being movable in response to fluid pressure at said inlet port inexcess of a first predetermined value and less than a secondpredetermined value from a position interrupting pressure fluidcommunication through one of said passage means toward a positioneffecting metered pressure fluid communication therethrough to establisha reduced fluid pressure at said outlet port in a predetermined ratiowith that at said inlet port when said metering valve is in a positioninterrupting pressure fluid communication through the other of saidpassage means, said metering valve being thereafter movable from itspressure fluid communication interrupting position in said other passagemeans in response to fluid pressure at said inlet port in excess of thesecond predetermined value and reduced fluid pressure at said outletport acting thereon toward a position effecting metered pressure fluidcommunication through said other flow passage to increase the reducedfluid pressure at said outlet port in another predetermined ratio withthat at said inlet port predeterminately greater than said first namedpredetermined ratio when said proportioning valve is in its pressurefluid communication interrupting position, and said metering valveincluding means responsive to the fluid pressures at said inlet andoutlet ports of a third predetermined value to move said metering meanstoward an open position in said other passage means effecting unmeteredpressure fluid communication therethrough between said inlet and outletports.
 14. A control valve comprising a housing having inlet and outletports therein, first and second passage means in said housing andrespectively connected in parallel flow relation between said inlet andoutlet ports, first and second valve seats in said housing about saidfirst and second passage means, first and second piston means movable insaid first and second passage means for controlling pressure fluidcommunication therethrough between said inlet and outlet ports,respectively, first and second valve means on said first and secondpiston means for engagement with said first and second valve seats,first and second spring means engaged with said first and second pistonmeans, said second spring means urging said second piston means toward aposition engaging said second valve means with said second valve seatfor interrupting pressure fluid communication through said secondpassage means between said inlet and outlet ports, said first pistonmeans being initially movable against said first spring means inresponse to fluid pressure at said inlet and outlet ports of a firstpredetermined value to engage said first valve means with said firstvalve seat interrupting pressure fluid communication between said inletand outlet ports through said first passage means and said first pistonmeans also being thereafter further movable assisted by said firstspring means in response to fluid pressure at said inlet port in excessof the first predetermined value and less than a second predeterminedvalue to disengage said first valve means from said first valve seateffecting metered pressure fluid communication through said firstpassage means between said inlet and outlet ports and establishing ametered fluid pressure at saiD outlet port in a first predeterminedratio with that at said inlet port when said second piston means is inits pressure fluid communication interrupting position, a pair ofeffecting areas on said second piston means respectively subjected tothe fluid pressures at said inlet and outlet ports, said second pistonmeans being movable from its pressure fluid communication interruptingposition against said second spring means in response to the fluidpressure at said inlet port in excess of the second predetermined valueacting on one of said areas and the reduced metered fluid pressure atsaid outlet port acting on the other of said areas to disengage saidsecond valve means from said second valve seat effecting meteredpressure fluid communication between said inlet and outlet ports throughsaid second passage means and establishing an increased metered fluidpressure at said outlet port in a second predetermined ratio with thatat said inlet port wherein said second predetermined ratio ispredeterminately greater than said first predetermined ratio when saidfirst piston means is in its pressure fluid communication interruptingposition, and said second piston means also being further movableagainst said second spring means to disengage said second valve meansfrom said second valve seat and establish open pressure fluidcommunication through said second passage means between said inlet andoutlet ports when the fluid pressure at said inlet port and the meteredfluid pressure at said outlet port acting on said one and other areasattain a third predetermined value predeterminately greater than saidsecond predetermined value, respectively.
 15. A fluid pressure systemcomprising a friction device, a fluid pressure source for energizingsaid friction device, a pair of modulating means in parallel flowrelation in said system for performing modulating operations on fluidpressure supplied from said source to said friction device underpreselected conditions, each of said modulating means being generallyoperable to interrupt the parallel flow relation when the other thereofis performing its modulating operation, respectively.
 16. A fluidpressure system comprising at least one friction device, a fluidpressure source for supplying fluid pressure to said friction device toeffect energization thereof, a pair of modulating means connectedbetween said source and friction device in parallel flow relation forperforming modulating operations on fluid pressure supplied from saidsource to said friction device under preselected conditions, each ofsaid modulating means being generally operable to interrupt the parallelflow relation upon the modulating operation of the other thereof toeffect the application to said friction device of the supplied fluidpressure in different predetermined ratios, respectively, and one ofsaid modulating means including means responsive to the supplied fluidpressure in excess of a predetermined value to obviate the modulatingoperation of said one modulating means.
 17. A fluid pressure systemcomprising at least one fluid pressure responsive brake device, meansincluding a fluid pressure source for supplying fluid pressure to saidbrake device to effect energization thereof, proportioning means andmetering means connected in parallel flow relation with each otherbetween said source and brake device for performing proportioning andmetering operations on the supplied fluid pressure and for interruptingsaid parallel flow relation under preselected conditions, respectively,said proportioning means being operable generally in response to thesupplied fluid pressure between first and second predetermined values toeffect the application to said brake device of a reduced fluid pressurein a predetermined ratio with the supplied fluid pressure when saidmetering means is interrupting said parallel flow relation, saidmetering means being thereafter generally operable in response to thesupplied fluid pressure in excess of the second predetermined value andthe applied fluid pressure acting thereon to effect a metered increasein the applied fluid pressure in another predetermined ratio with thesupplied fluid pressure predeterminately greater than the first namedpredetermined ratio when said proportioning means is interrupting saidparallel flow relation, and said metering means including meansresponsive to the supplied and applied fluid pressures of a thirdpredetermined value predeterminately greater than the secondpredetermined value for obviating the metering operation of saidmetering means and effecting an unmetered flow of the supplied fluidpressure to said brake device.